Smart Pd Catalyst with Improved Thermal Stability Supported on High-Surface-Area LaFeO₃ Prepared by Atomic Layer Deposition

Abstract

The concept of self-regenerating or "smart" catalysts, developed to mitigate the problem of supported metal particle coarsening in high-temperature applications, involves redispersing large metal particles by incorporating them into a perovskite-structured support under oxidizing conditions and then exsolving them as small metal particles under reducing conditions. Unfortunately, the redispersion process does not appear to work in practice because the surface areas of the perovskite supports are too low and the diffusion lengths for the metal ions within the bulk perovskite too short. Here, we demonstrate reversible activation upon redox cycling for CH oxidation and CO oxidation on Pd supported on high-surface-area LaFeO, prepared as a thin conformal coating on a porous MgAlO support using atomic layer deposition. The LaFeO film, less than 1.5 nm thick, was shown to be initially stable to at least 900 °C. The activated catalysts exhibit stable catalytic performance for methane oxidation after high-temperature treatment.

Atomic Layer Deposition on Porous Materials: Problems with Conventional Approaches to Catalyst and Fuel Cell Electrode Preparation

“…For many potentially interesting precursors, the ligands cannot be easily removed in this temperature range. An example of this occurred with the precursor used in a recent study to deposit La 2 O 3 , La(TMHD) 3 (Tris(2,2,6,6-tetramethyl-3,5-heptanedionato) lanthanum) [36][37][38]. The organic ligands on this molecule are not removed by water or O 2 at ALD conditions, and are oxidized by ozone only very slowly.…”

“…The ALD approach is also applicable to mixed oxides, such as for example CeO 2 -ZrO 2 mixed oxides, by alternating suitable Ce and Zr precursors during ALD cycles [73,85]. Although high surface area perovskites can be prepared by combustion synthesis [86,87], LaFeO 3 films with the perovskite structure were also prepared by ALD [38].…”

Atomic layer deposition of perovskites part 2: Designing next generation electronic applications

“…Lanthanum‐based perovskites deposited using ALD have been studied extensively for different applications . Recently, ALD deposited Pd doped LaFeO 3 was studied as a smart catalyst which undergoes efficient redox cycling . ALD was instrumental because of its ability to deposit highly conformal layers on high surface area supports, such as porous structures (Figure B), thus opening new avenues for research and development in the field of thermo‐chemical splitting of CO 2.…”

“…This is especially true when one seeks to elucidate mechanistic information of ALD perovskite films and to understand how certain parameters affect its growth and its properties. As the use of synchrotrons has been on the rise to characterize ALD thin films, there still lacks any meaningful number of papers on ALD perovskites . XAS is a sensitive, element specific technique that can be used to get local electronic and geometric structure information of materials, similar to EELS, however with several key advantages .…”

“…21 Recently, ALD deposited Pd doped LaFeO 3 was studied as a smart catalyst which undergoes efficient redox cycling. 22 instrumental because of its ability to deposit highly conformal layers on high surface area supports, such as porous structures ( Figure 5B), thus opening new avenues for research and development in the field of thermo-chemical splitting of CO 2. 23 There are still challenges with perovskites with regards to chemical stability and low enthalpies, which needs to be addressed.…”